Investigators have learned that James Holmes, the man accused of perpetrating the largest massacre in American history, had received a significant number of commercial deliveries to his home and office, as they try to build a picture of the alleged shooter and the events leading up to the largest mass shooting in American history.

Bomb techinicians spent much of the morning making Holmes' Aurora, Colo., apartment safe to enter, and investigators then worked into the evening collecting evidence and securing the scene, said Jim Yacone of the FBI.

After 7 p.m. local time, residents in neighboring buildings were allowed back into their homes for the first time since early Friday morning, though tenants in Holmes' building will have to wait until Sunday.

"An extensive amount of evidence" is being collected and will be sent to the FBI's crime lab in Quantico, Va., Yacone said.

Authorities conducted a controlled detonation today as they slowly entered the booby-trapped apartment, which authorities said was "set up to kill."

"It was an extremely dangerous environment. If [someone] had walked in that door, they would have sustained significant injuries or lost their life," Yacone said.

A robot driven by a bomb technician and dynamic destruction tools were used to slowly and methodically disable explosive devices while also preserving evidence, Yacone said.

A loud pop was heard, but there was no visible smoke or fire at the scene. The street outside the apartment was shut down and residents were notified of the explosion by a reverse 911 call.

Police said Friday that a large number of explosive devices and trip wires were found at Holmes' apartment in an "elaborate" set-up.

One official told ABC News there were wires everywhere and described Holmes as a like a mad scientist.

Some devices appeared to be strapped to boxes of bullets and what looked like mortar rounds, police said.

The "flammable and explosive" materials could have blown up Holmes' apartment building and the ones near it, police said.

After a thorough search of Holmes' apartment, police moved into the investigation phase, hoping Holmes' computer -- if he has one -- and any writings could provide a gateway to understanding his motive.

A former doctoral student, Holmes is suspected of killing 12 people at the screening of the latest Batman movie in Aurora early Friday morning. Fifty-eight people were wounded.

Authorities have finished sweeping the Century 16 theater and plan to turn it over to Holmes' defense on Tuesday and back to theater owners on Wednesday, Oates said.

Personal belongings that were left behind amid the chaos and carnage were recovered by Aurora police, who plan to work with victims advocates to help reuunite people who were in the theater that night with their belongings, providing there is no forensic link, Oates said.

Among the dead include Micayla Medek, 23; Alex Sullivan, 27, who was attending the movie for his birthday; Ohio native Matt McQuinn; and Alex Teves, 24.

Two other people died at the hospital, including 24-year-old aspiring sportscaster Jessica Ghawi. Police said 30 people remained hospitalized with 11 of them in critical condition. Bullets from the shooting spree tore through the theater and into adjoining theaters, where at least one other person was struck and injured.

John Larimer, a member of the Navy, was also confirmed by his family to be among the dead. The family said they were notified at their Illinois home around midnight today by a Navy notification team that Larimer was dead.

Veronica Moser, 6, was killed, according to The Associated Press. The girl's mother, Ashley Moser, 25, is in critical condition after she was shot in the throat and abdomen, said her aunt, Annie Dalton.

Oates announced Friday that Holmes had purchased four guns at local shops and more than 6,000 rounds of ammunition on the Internet in the past 60 days.

"All the ammunition he possessed, he possessed legally, all the weapons he possessed, he possessed legally, all the clips he possessed, he possessed legally," an emotional Oates told reporters.

The chief said "he could have gotten off 50 to 60 rounds, even if it was semi-automatic, within one minute," Oates said.

Eyewitness Accounts

Eyewitness and victim accounts of the mass shooting in the packed movie theater paint a picture of panic and horror.

Eric Hunter said this morning that he was in an adjacent theater to where the shooting took place, when bullets "came right through the walls."

"When the first three shots rang out, we didn't know if it was part of the movie or not," he said. "I saw blood on the stairs and I turned to the crowd and said there's something wrong and we need to call the cops."

Hunter then said he made his way to the emergency exit door, where he saw two teen girls outside, one of whom had been hit by bullet and was asking for help. That's when Hunter said he saw the shooter.

"I saw the gunman coming around the corner so I held the door for about five seconds," Hunter said. "He's banging on the door, banging on the door... I didn't know if he was going to shoot the door. I didn't know what he had."

Holmes allegedly entered the movie auditorium wearing a ballistics helmet, bulletproof vest, bulletproof leggings, gas mask and gloves. He detonated multiple smoke bombs, and then began firing at viewers in the sold-out auditorium, police said Friday.

Holmes, who is being held in jail and will make his first court appearance Monday, is originally from Riverside, Calif., where he attended the University of California branch, Oates said Friday.

"Neighbors report that he lived alone and kept to himself," he added.

Holmes was apprehended within minutes of the 12:39 a.m. shooting at his car behind the theater, where police found him in full riot gear and carrying three weapons, including an AR-15 assault rifle, which can hold upwards of 100 rounds, a Remington 12-gauge shotgun, and a .40 Glock handgun. A fourth handgun was found in the vehicle.

Agents from the federal bureau of Alcohol, Tobacco, and Firearms are tracing the weapons.